I think that building nuclear (maybe renewable) powered desalinization plants along the coast is the only answer. Fill existing coastal reservoirs from desal. Stupid to pump from the mountains to the coast where all the people are. The dams we have are sufficient for flood control and agriculture.
“The dams we have are sufficient for flood control and agriculture.”
Your premise is correct once you have the desalinization infrastructure to satisfy the bulk of your water needs. That said, using desal (because it’s more costly than impounding rainwater) as a bootstrap to your normal water system probably makes more sense because unless we are actually going to see a trend that says we will receive over the years less rain, we will not always need it.
Of course for California, getting rid of a few million illegals would be the most cost-effective way to help fix the problem.